Distribution centers use relatively common processes to pick products and load trucks with those products, for delivery to other locations. These products are typically stacked or otherwise arranged to form a load. The products may be placed on a pallet, forming a palletized load. A pallet is normally constructed with a top plate and at least a partial bottom plate. For example, the bottom plate may include a plurality of boards spaced apart from one another. The bottom plate supports the palletized load when it is stacked on top of another load. Pallets are preferably constructed of wood, but alternatively may be made of plastic. Plastic pallets generally have a series of “legs” rather than a bottom plate. The pallets are typically constructed to industry standards. Sometimes, pallets may be leased from a pallet supplier.
A palletized load can be carried on tines of a fork of a pallet truck. The tines are cantilevered off of the pallet truck, but may include retractable wheels on or near their distal ends. When retracted, the retractable wheels may be contained within the tines or otherwise flush with the external surfaces of the tines. With the retractable wheels in their retracted positions, the tines of the fork can be more easily inserted into and extracted from tunnels or holes located between the top and bottom plates of the pallet. After the tines are inserted through the tunnels, the retractable wheels may be, for example, hydraulically lowered. As the retractable wheels pass through openings in the bottom plate of the pallet and engage the ground, a lifting force is exerted on the top plate of the pallet by the tines of the fork, thus raising the palletized load off of the ground. When the palletized load is ready for dropping off, the retractable wheels are retracted, causing the tines of the fork to lower, thus lowering the palletized load toward the ground.
Often times, palletized loads are wrapped for transportation, storage, containment, stabilization, protection, and waterproofing. Various packaging techniques and wrapping apparatuses have been used to wrap palletized loads. One system uses stretch wrapping machines to stretch, dispense, and wrap stretch packaging material around a palletized load. Stretch wrapping can be performed as an inline automated packaging technique which dispenses and wraps packaging material in a stretched condition around products arranged on a pallet to cover and contain the products. Stretch wrapping, whether accomplished by turntable, rotating arm, or rotating ring, typically covers the vertical sides of the palletized load with a stretchable film such as polyethylene film. In each of these arrangements, relative rotation is provided between the palletized load and a packaging material dispenser to wrap packaging material about the sides of the palletized load.
Palletized loads must somehow be transported to the wrapping apparatus, and then placed in a wrapping area of the wrapping apparatus. In order to increase efficiency and reduce the number of bottlenecks, conventional conveyors may be used to transport unwrapped palletized loads to the wrapping areas of the wrapping apparatuses. By using conveyors, pallet trucks can be more efficient since they can drop loads off at the conveyor and then leave to pick up other loads, allowing the conveyor to transport waiting loads to a wrapping area. Using conventional conveyors, however, may present problems. One problem is that pallet trucks are unable to lift the unwrapped palletized loads high enough to place them onto conventional above-floor conveyors. Conveyors with lift tables or elevators are available to automate the process. However, such devices require a large amount of space and are mechanically complex and costly to maintain. In addition, conveyors have been placed in pits created in the floor to lower the conveyor to be approximately level with the floor. This requires a large amount of space and the permanent destruction of the floor. In addition, such a process is costly.
Ramp type solutions, including those having a ramp leading up to a level conveyor, have not proven feasible due to the type of lift mechanisms found on pallet trucks. The tines of a pallet truck fork are typically around 3 inches thick, and occupy most of the space between the top and bottom plates of pallets (the space being around 3.5 to 4.5 inches, typically). When a pallet truck's front wheels are retracted to assist with extraction of the tines from a pallet's tunnels, the bottom surfaces of the tines will lower. If the fork is lowered to place a palletized load on a level conveyor while the pallet truck is on a ramp, the lowering of the tines can cause the tines to wedge against the top and/or bottom plates of the pallet in the pallet's tunnels, thus binding the tines to the pallet, due at least in part to misalignment between the tines and the surface of the level conveyor. FIG. 1 shows a fork in various states of insertion in a pair of pallets. The fork wedges against the top plates of the pallets as it moves between a state in which the fork is partially inserted and a state in which the fork is fully inserted. The position of the fork at full insertion is represented in FIG. 1 by the tip portion of the fork on the left (near a middle section of the leftmost pallet). Accordingly, due to the widespread use of pallet trucks, manufacturers have not been able to successfully employ either powered or non-powered conveyors to automated wrapping operations, and distribution centers have not been able to fully harness efficiency gains associated with using conveyors and automate wrapping operations.
Solutions requiring conveyor cut-outs, as demonstrated in FIG. 2, have not proven feasible for pallets with bottom plates. One reason is that as a pallet with a bottom plate is loaded onto the conveyor, the pallet truck's fork may continue down into the cutout while moving to its lowered position. This movement of the fork may break the portion of the bottom plate positioned above the cut-out, since the fork will force that portion into the cut-out while the conveyor supports the side portions of the pallet at a height higher than the cutout. Dropping the conveyor to floor-height to avoid this breaking is not desirable for at least the reasons discussed above.
In light of these drawbacks, there is a need to reduce the complexity, time, and number of material handling steps necessary to move palletized loads to and from a wrapping apparatus in a simple, reliable, and inexpensive manner.